Map displaying method and apparatus, and navigation system having the map displaying apparatus

ABSTRACT

The present invention is related to a stereoscopic map displaying method beneficial for a navigation system in which map information is selected from a database according to a current location of a mobile object. The map database for storing map information comprises a plurality of types of information regarding a first map mesh provided with height information and a second map mesh with no height information wherein there is provided information for identifying that the second map mesh has no height information. A mode of a mark representing the moving display device is switched in accordance with a result whether first map data or second map data is utilized and displayed on the display apparatus superposing graphics data.

This is a continuation of application Ser. No. 09/640,522 now U.S. Pat.No. 6,341,254 filed Aug. 17, 2000, which is a continuation ofapplication Ser. No. 08/963,607 filed Oct. 31, 1997, which was issued asU.S. Pat. No. 6,175,802 on Jan. 16, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a map displaying method andapparatus, and a navigation system having such a map displayingapparatus. Particularly, the present invention is related to astereoscopic map displaying method beneficial for the navigation systemin which map information is selected from a map database according to acurrent location of a mobile object such as an automobile, and aperspective map viewing the ground surface along a direction angled tothe ground surface is displayed.

2. Description of Related Art

The navigation system is known as an apparatus which assists a driver ofan automobile by fetching digital map data stored in storage media suchas CD-ROM, displaying a map showing buildings, roads and the like on adisplay screen, and superposing a current location of the automobile anda direction toward its destination on the map, which are detected byvarious sensors such as GPS.

A recent navigation system, such as disclosed in Japanese PatentApplication Publication (KOKAI) No. 2-244188, uses a pseudo threedimensional display method in which a coordinate transformation of twodimensional map information is executed to generate a pseudo threedimensional image so as to display the map information in the vicinityof the current automobile location in a more easily recognizable manner.The pseudo three dimensional display may give a kind of threedimensional impression to a viewer using the two dimensional mapinformation because, in the pseudo three dimensional display, a viewpoint is set at a predetermined position above the automobile, and aperspective image viewed along a viewing direction which makes an acuteangle with respect to the ground plane is displayed.

The pseudo three dimensional display of the prior art is generated fromthe two dimensional map information using the view point determinedwhile assuming a flat ground surface. This may cause some problems ifthe stereoscopic map display method mentioned above is executed usingthree dimensional map information including information regarding atopographical elevation, instead of the two dimensional map information.

Namely, the three dimensional map information contains topographicalinformation such as elevations of mountains, buildings or the like. Ifsuch three dimensional information is used and the view point isestablished with respect to the ground plane at sea level (altitude of 0m) in the same way as that of the pseudo three dimensional displaymethod, the established view point may end up inside a mountain whichprotrudes above the ground plane, depending on its height. If that isthe case, the navigation system may not be able to display a location ofthe automobile or carry out the navigation procedure.

SUMMARY OF THE INVENTION

The present invention is invented in light of the above mentionedproblems, and has an object to provide a map display method andapparatus which enable a stereoscopic map display using threedimensional map data including information indicating horizontallocations of map constituent elements such as topographical features,roads, buildings, and information indicating heights or elevations oraltitudes of at least some of the map constituent elements which arelocated in at least a part of the available horizontal map area.

Another object of the present invention is to provide a navigationsystem having a stereoscopic map display function which enables renewalof contents of the display smoothly with movement of a vehicle even withthe topographic variation or ups and downs of roads.

The above objects of the present invention are accomplished by a mapdisplay method in which map information in an area specified in responseto a current location of a moving object is read from a map database; aperspective map viewed from a view point toward a ground plane isgenerated by executing coordinate transformation procedures on the mapinformation; and a scenery image corresponding to the perspective map isdisplayed on a display device, wherein the view point for generating theperspective map is established above a height of a map constituentelement existing at a location specified in response to the currentlocation of the moving object, and the height of the view point isrenewed with movement of the moving object.

Further, the above objects of the present invention are accomplished bya map display method in which a perspective map is generated using mapinformation in an area specified in response to a location indicated byinput location information, and a scenery image corresponding theperspective map is displayed, wherein a map database which contains themap information includes information regarding heights of mapconstituent elements existing at least in a part of the available maparea; a view point for generating the perspective map is establishedabove a height of a map constituent element existing at a map locationspecified in response to the location indicated by the input locationinformation when information regarding the height of the constituentelement is available; and the height of the view point is reestablishedwhen new input information is provided.

Further, the above objects of the present invention are accomplished bya map display apparatus in which a perspective map is generated from mapinformation in an area specified in response to a location indicated byinput location information; and graphic data for displaying a sceneryimage corresponding the perspective map is outputted; comprising a viewpoint setting unit for establishing at least a height of the view pointamong variables to be set to generate the perspective map, and a displayprocessing unit for generating the graphic data for displaying thescenery image corresponding the perspective map generated in response tothe view point set by the view point setting unit, wherein the viewpoint setting unit establishes a height of the view point above anelevation of a topographical feature at a map location which isspecified in response to the location indicated by the input locationinformation when information regarding the elevation of topographicalfeature is available.

Further, the objects of the present invention are accomplished by anavigation system comprising a map database device, a current locationdetection device, a map display device for generating a perspective mapfrom map information in an area specified in response to the currentlocation of an automobile, and generating graphic data for displaying ascenery image corresponding the perspective map, and a display device,wherein the map display device comprises a view point setting unit forexecuting at least a setting procedure of the view point among variablesto be set for generating the perspective map, and a display processingunit for generating graphic data for displaying a scenery imagecorresponding to the perspective map generated in response to the viewpoint established by the view point setting unit, and the view pointsetting unit establishes a height of the view point above an elevationof a topographical feature at a map location which is specified inresponse to the detected current location of the automobile wheninformation regarding the elevation of a topographical feature isavailable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a construction of the navigationsystem in an embodiment of the present invention;

FIG. 2 is a block diagram showing a hardware construction of anoperation and processing unit 1-1 of FIG. 1;

FIG. 3 is a block diagram showing a functional construction of theoperation and processing unit 1-1 of FIG. 1;

FIG. 4 is an explanatory illustration showing an example of astereoscopic display according to a display method of the presentinvention;

FIG. 5 is a block diagram for illustrating data flows in the displaymethod of the present invention;

FIG. 6 is an explanatory illustration showing a concept of thecoordinate transformation in the map display;

FIG. 7 is a flowchart for illustrating a view point setting method,which is a feature of the present invention;

FIG. 8 is an explanatory illustration for supplementing FIG. 7;

FIG. 9 is a flowchart for illustrating the view point setting methodwhich changes a line of sight according to movement of the vehicle;

FIG. 10 is a flowchart for illustrating the view point setting methodwhich fixes a height of the view point when an area has an almost a flattopographical feature;

FIG. 11 is an explanatory illustration showing a concept of the viewpoint setting method which establishes the view point inside of thevehicle;

FIG. 12 is an explanatory illustration showing an example of the displaywhen the view point is set inside the vehicle;

FIG. 13 is a flowchart for illustrating the view point setting methodwhich switches the view point to inside or outside of the vehicleaccording to a height of the view point;

FIG. 14 is a flowchart for illustrating the view point setting methodwhich switches the view point to inside or outside of the vehicleaccording to a scale of the display;

FIG. 15 is a flowchart for illustrating the view point setting methodwhich varies a view angle according to a view angle selection ofNormal/Wide;

FIG. 16 is a flowchart for illustrating the view point setting methodwhich varies a height of the view point according to a display methodselection of the pseudo three dimensional display/the three dimensionaldisplay;

FIG. 17A is an explanatory illustration showing relative locations ofthe vehicle and the view point in the three dimensional display;

FIG. 17B is an explanatory illustration showing relative locations ofthe vehicle and the view point in the pseudo three dimensional display;

FIG. 18 is a flowchart for illustrating the view point setting methodwhich varies a height of the view point according to a selection ofScroll or not;

FIG. 19 is an explanatory illustration showing an example of a dataformat of the map database according to the present invention;

FIG. 20 is a flowchart for illustrating the view point setting methodwhich varies a height of the view point according to whether informationregarding elevations of the topographical features are available or not;

FIG. 21 is a flowchart for illustrating the view point setting methodwhich varies a height of the view point according to whether informationregarding elevations of the roads are available or not;

FIG. 22 is an explanatory illustration for supplementing FIG. 21;

FIG. 23A is an display example of the vehicle when the view point is setat a higher position;

FIG. 23B is an display example of the vehicle when the view point is setat a lower position; and

FIG. 24 is a block diagram showing a construction of a map displayapparatus in another embodiment of the present invention.

FIG. 25 is a flowchart for illustrating another embodiment of the viewpoint setting method of FIG. 13.

FIG. 26 is a flowchart for illustrating another embodiment of the viewpoint setting method of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described withreference to the figures.

As shown in FIG. 1, a navigation system according to the embodimentcomprises, for example, an operation and processing unit 1-1, a displaydevice 1-2, a map database unit 1-3, a voice input/output device 1-4,and an input device 1-5.

The operation and processing unit 1-1 is a main unit for variousprocessing such as detecting a current location of the vehicle based onoutput information from sensors 1-7-1-10 which will be described later,graphically developing a map image from the map information which isnecessary for the display and read from the map database unit 1-3 incorrespondence with the detected current location of the vehicle, andsuperposing a vehicle symbol on the map image for indicating the currentlocation of the vehicle which is detected by the sensors 1-7-1-10; orcalculating the best fitted route to a location requested by a user viathe input device 1-5 (for example, from the current location to adesignated destination), and guiding the user along the best fittedroute using the voice input/output device 1-4 and/or the display device1-2.

The display device 1-2 is a unit for displaying the graphic informationgenerated in the operation and processing unit 1-1, and comprises a CRTor a liquid crystal display device or the like. Typically, an RGB signalor NTSC (National Television System Committee) signal is used for a S1signal connecting the operation and processing unit 1-1 and the displaydevice 1-2.

The map database unit 1-3 comprises a storage medium with a largecapacity such as CD-ROM, a IC card or DVD (Digital Video Disc), andcarries out read/write processing of the necessary map data. The voiceinput/output device 1-4 transforms a message for the user, which isgenerated by the operation and processing unit 1-1, to a voice signaland outputs the voice signal, as well as recognizing a user's voice andtransferring its content to the operation and processing unit 1-1.

The input device 1-5 is a unit for accepting various operation commands,which will be described later, from the user, and comprises hardwareswitches such as a scroll key for scrolling the displayed map, a scalechange key for changing a scale of the displayed map, a joystick, and atouch panel disposed on the display screen.

The system of the embodiment further comprises sensors to be used fordetecting a current location of the vehicle in a moving vehiclenavigation operation, such as a wheel rotation speed sensor 1-7 formeasuring a distance by multiplying a detected rotation rate of thewheel by a circumference of the wheel; an azimuth sensor 1-8 fordetecting an azimuth on which the vehicle is heading by measuring ageomagnetic field of the earth; a gyro sensor 1-9 for detecting arotation angle of the vehicle comprising an optical fiber gyro or anoscillating gyro; a GPS receiver 1-10 for determining the currentlocation, the heading direction and the heading azimuth of the vehicleby receiving signals from three or more GPS satellites simultaneouslyand measuring ranges and range rates between the vehicle and the GPSsatellites.

The system of the embodiment further comprises a traffic informationreceiver 1-11 for receiving signals from an FM multiplex broadcaststation or a beacon transmitter which transmits a traffic informationsignal regarding traffic congestion, road construction or road closures,available parking, and the like. Further, the system comprises a vehicleLAN device 1-6 for receiving various information about the vehiclestatus such as open/close of doors, status and types of the lights whichare turned on, status of engine, and a result of a problem diagnosisoperation.

FIG. 2 shows an example of a hardware structure of the operation andprocessing unit 1-1.

The operation and processing unit 1-1 comprises the following deviceswhich are interconnected to each others through a bus. These constituentdevices are a CPU 2-1 executing various operations such as a numericaloperation or a control of the devices, a RAM 2-2 storing map data oroperation data, a ROM 2-3 storing programs or data, a DMA (Direct MemoryAccess) 2-4 for executing a high speed data transfer between thememories and between the memory and the device, a graphic controller 2-5executing various graphic imaging operations such as development ofvector data to pixel information and control of the display operation, aVRAM 2-6 storing graphic image data, a color palette 2-7 converting theimage data to the RGB signal, an A/D converter 2-8 converting an analogsignal to a digital signal, a SCI 2-9 converting a serial signal to abus-synchronized parallel signal, a PIO 2-10 sending the signal on thebus while synchronizing with the parallel signal, and a counter 2-11accumulating a pulse signal.

FIG. 3 shows a functional structure realized by the operation andprocessing unit 1-1 having the hardware structure mentioned above. Eachof the functional blocks will now be described.

A current location detection unit 3-5 executes operations to obtain alocation of the vehicle after its movement (X′,Y′) from an initiallocation (X,Y) using range and angle data obtained by integrating rangepulse data S5 measured at the wheel rotation speed sensor 1-7 andangular acceleration data S7 measured at the gyro 1-9, and furthertime-integrating these data. Further in the location calculation unit3-5, the absolute azimuth on which the vehicle is heading is correctedusing the azimuth data S6 from the azimuth sensor 1-8 and the angle dataobtained by integrating the angular acceleration data S7 from the gyro1-9 so as to bring the rotation angle of the vehicle and the movingazimuth into agreement. Further, the current location detection unit 3-5may output information regarding the current location of the vehicle,after executing an operation, which cancels out errors accumulated inthe data outputted from the above mentioned sensors due to their dataintegration operations, using location data S8 which is periodicallyobtained at the GPS receiver at a certain period when the location dataS8 is available.

Information regarding the current location obtained in this way containserrors originated in the sensor data. Thus, a map match processing unit3-6 is provided to further increase accuracy in detecting the currentlocation of the vehicle. The map match processing unit 3-6 executesoperations such as comparing road data, which is included in the map inthe vicinity of the current location of the vehicle read by the dataread unit 3-7, and a trajectory of the vehicle obtained from the currentlocation detection unit 3-5, and correcting the current location so thatthe corrected location gives the best correlation between shapes of theroad data and the vehicle's trajectory. In many cases, the map matchingprocess enables fitting of the current location into a road on which thevehicle is actually moving, and thus outputting of a precise currentlocation of the vehicle.

The information regarding the current location of the vehicle is storedin a trajectory memory unit 3-8 every time the vehicle has moved acertain distance. The trajectory data is used to generate a graphicimage for marking the trajectory of vehicle on roads of thecorresponding map, where the vehicle had traveled.

A command decoder unit 3-1 accepts requirements (commands) from a userthrough the input device 1-5, analyzes contents of the requirements, andcontrols each of the units so as to execute operations in response tothe contents. For example, when the user requests a route guidance to adestination, the command decoder unit 3-1 requests a display processingunit 3-10 to carry out operations to display a map for setting thedestination, and further requests a route calculation unit 3-2 to carryout operations to calculate a route from the current location to thedestination.

The route calculation unit 3-2 searches for a route between thedesignated locations from the map data using the Dijkstra algorithm orthe like, and stores the route in a route memory unit 3-3. The routecalculation unit 3-2 may calculate several types of routes such as theshortest route between the designated locations, a route which isreachable within the shortest travel time, and the most inexpensiveroute.

A route guidance unit 3-4 compares link information for the routeguiding stored in the route memory unit 3-3 with the current vehiclelocation information obtained in the current location detection unit 3-5and the map match processing unit 3-6, and guides the user by vocallynotifying whether or not to go straight or turn left/right using a voiceinput/output device 1-4 a predetermined period of time before thevehicle pass through an intersection, or superposing a mark indicating adirection in which the vehicle should be directed on the map displayedon a screen of the display device 1-2.

The data read unit 3-7 is operated to fetch and prepare map data of arequested area from the map database unit 1-3.

The view point setting unit 3-11 is one of characteristic features ofthe present invention, which establishes variables such as a view point,a line of sight, a view angle, which should be established for the mapdisplay method of the present invention.

The display processing unit 3-10 receives the map data in the vicinityof a location which is requested to be displayed from the data read unit3-7, develops the map data into a graphic image using the view point/theline of sight/the view angle established by the view point setting unit3-11 and using a display scale, an imaging method, an imaging azimuthdesignated by the command decoder unit 3-1, and transfers the developedgraphic image to the VRAM 2-6. A menu display unit 3-9 accepts variousrequests output from the command decoder unit 3-1, and transfers imagesof various types of menus or symbols which are requested to the displayprocessing unit 3-10 for superposing the images on the displayed map.

FIG. 4 shows an example of the stereoscopic map display, which isdisplayed by the device of the present embodiment and in which a part ofthe map data such as topographical features, roads, etc. are graphicallydeveloped into an image to be displayed. There, 4-2 is a mountain drawnbased on the topographic elevation data (altitude data), 4-3 is roadswhich are line-drawn using a fixed width, and 4-4 is a symbol indicatingthe current location of the vehicle. The display example 4-1 isgenerated by reading out the map data in the vicinity of the currentlocation of the vehicle from the map database unit 1-3 based on thecurrent location of the vehicle output from the sensor system, anddisplaying a scenery image (perspective map) viewed from a view pointestablished above the vehicle in the air using a method of the presentinvention.

FIG. 5 shows an example of a data flow when a stereoscopic map like theone in FIG. 4 is displayed.

The data read unit 3-7 reads out the map data in the vicinity of thevehicle's current location from the map database unit 1-3 based on thecurrent location of the vehicle detected at the current locationdetection unit 3-5. The view point setting unit 3-11 reads the currentlocation of the vehicle detected at the current location detection unit3-5 and the map data containing topographical features, roads, buildingsfrom the data read unit 3-7, and establishes variables such as the viewpoint, the line of sight, the view angle, etc. which should beestablished for the stereoscopic map display.

The display processing unit 3-10 carries out a coordinate transformationof the map data in the vicinity of the vehicle according to the viewpoint, the line of sight and the view angle established by the viewpoint setting unit 3-11, and generates the perspective map image to bedisplayed. The map match processing unit 3-6, which obtains thevehicle's current location with a higher accuracy and inputs theaccurate current location to the view point setting unit 3-11 and thedisplay processing unit 3-10 as shown in FIG. 3, is omitted here in FIG.5, assuming that the current location detection unit 3-5 can obtain thecurrent location of the vehicle with a high enough accuracy.

The coordinate transformation operation used in the display method ofthe present embodiment will now be described with reference to FIG. 6.

A perspective map 6-6 is generated by projecting a topographical feature6-2 situated above a ground plane 6-4 at sea level onto a screen (viewplane) 6-3 disposed between the view point (view reference point) 6-1and the topographical feature 6-2 through a series of coordinatetransformations. The series of coordinate transformations comprise, forexample, the first transformation for transforming the map dataexpressed in an object coordinate to that of a world coordinate, thesecond transformation for transforming the result of the firsttransformation into a view point coordinate whose origin is set at theview point 6-1, and the third transformation for transforming the resultof the second transformation into a screen coordinate so as to projectthe result of the second transformation onto the screen 6-3.

According to the series of coordinate transformations, the perspectivemap 6-6 in a screen window corresponding to a part of the topographicfeature may be generated depending on a spatial relationship between theview point 6-1 and the topographic feature 6-2. In the presentembodiment, the display device 1-2 displays a graphic image generatedusing data of the perspective map 6-6 so as to show scenery (a scenicimage) which is supposed to be seen when a part of the topographicfeature 6-5 is viewed from above in the air.

In this specification, “the ground plane at sea level” means a flatplane like the plane 6-4 shown in FIG. 6, and “the ground plane” means asurface of the ground plane like 6-2.

An example of the procedure in the view point setting unit 3-11 of thepresent embodiment will now be described with reference to FIGS. 7 and8. FIG. 7 is a flowchart of the procedure steps, and FIG. 8 is anexplanatory illustration for supplementing FIG. 7. In the following, alocation of the vehicle is assumed to be at a point 8-1.

First, the current location of the vehicle 8-1 is obtained from thecurrent location detection unit 3-5 or through the map match processingunit 3-6 (Step 7100). Then, a height (elevation) h_(t) at the currentlocation of the vehicle is calculated based on data regarding a heightof the topographical feature (elevation data), which are obtainedthrough the data read unit 3-7 (Step 7200). If the accuracy of data inthe height direction of GPS signal for detecting the current location ofthe vehicle is considered to be high enough, Step 7200 may be skipped.

Next, a predetermined height Y is added to the vehicle elevation h_(t)for calculating a view point height y_(v) so as to set the view pointabove the vehicle elevation h_(t) (Step 7300). In the Step 7400, it isdecided if the established view point is above the ground plane or notby comparing the view point height y_(v) and an elevation h_(v) at alocation which is behind the vehicle's current location with apredetermined separation distance L.

If it is decided that the view point is above the ground plane (Y atStep 7400), the view point 8-2 is finally established behind thevehicle's current location with the predetermined separation distance Land at the height y_(v) (Step 7600), and the line of sight of the viewpoint is set toward the vehicle's current location 8-1 (Step 7700). Ifthe view point is located under the ground plane (N at Step 7400), y_(v)is reset so as its value becomes larger than h_(v) (Step 7500), and thenthe operation procedure moves to Step 7600.

As described above, the present procedure enables setting and resettingof the height of the view point so that the view point is always locatedabove in the air while the vehicle is moving.

Alternatively, the view point height y_(v) (y_(v)′ at a location 8-3)may be set using a fixed height difference Y between the vehicle and theview point as the vehicle moves from the location 8-1 to the location8-3 as shown in FIG. 8. This makes it possible to fix a relative spatialrelationship between the vehicle's location and the view point.

According to the procedure shown in FIG. 7, the spatial relationship maybe maintained in a normal situation, and the location of the view pointmay be set always above in the air by executing an exceptional step likeStep 7500 even when there is a large amount of the topographicalvariation.

It is obvious that the setting method of the view point height in thepresent embodiment may be also applicable in the same way as mentionedabove even when the topographical elevation or the road elevation isless than sea level, i.e. even when the elevation values are less thanzero.

Another embodiment of the procedure of the view point setting unit 3-11of the present invention will now be described with reference to FIG. 9.

In the present embodiment, procedure steps for displaying the vehicleand scenery around the vehicle while changing the view point withmovement of the vehicle are added to the procedure of FIG. 7. Steps7110, 7210, 7710 of the present procedure are the same as Steps 7100,7200, 7700 of FIG. 7 respectively except that the current location ofthe vehicle in the present embodiment is assumed to be at the location8-3 of FIG. 8.

In the present procedure, the view point setting unit 3-11 obtains thecurrent location of the vehicle (Step 7110), calculates the vehicleelevation h_(t+dt) (Step 7210), obtains the previous view point 8-2(Step 7211), and calculates a distance d between the previous view point8-2 and the vehicle's current location 8-3 (Step 7212).

Further, it is decided if the distance d is within a predetermined rangeor not (Step 7213). If the distance d is within the predetermined range(Y at Step 7213), the same view point is maintained (Step 7214), andonly the line of sight is changed toward the new current location of thevehicle (Step 7710). If the distance d is larger than the predeterminedrange (N at Step 7213), the procedure proceeds to Step 7300 of FIG. 7.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIG. 10.

In the present embodiment, procedure steps for setting the view pointheight while judging its necessity of renewal based on an amount oftopographical variation around the vehicle's current location are addedto the procedure of FIG. 7. Steps 7110, 7210, 7710 of the presentprocedure are the same as Steps 7100, 7200, 7700 of FIG. 7 respectivelyexcept that the current location of the vehicle in the presentembodiment is assumed to be at the location 8-3 of FIG. 8.

In the present procedure, the view point setting unit 3-11 obtains thevehicle's current location 8-3 (Step 7110), calculates the vehicleelevation h_(t+dt) (Step 7210), obtains the previous view point heighty_(v) (Step 7211), calculates a height difference Δh between the vehicleelevation h_(t+dt) at its current location and the height of theprevious view point (Step 7221), and checks if the height difference Δhis within a predetermined range or not (Step 7222).

If the height difference Δh is within the predetermined range (Y at Step7222), the same height of the view point as the previous one ismaintained and the new view point 8-4 is established with this height(Steps 7223, 7710). If not, the procedure proceeds to Step 7300 of FIG.7.

The present procedure is required to be executed as the vehicle moves.Instead of the present procedure, it may be possible to divide the mapinto a plurality of meshes each having a predetermined map area, and toestablish the view point height to a fixed value within each of themeshes by evaluating an amount of the topographical variation within themesh. Alternatively, a section of roads where the view point height maybe fixed may be specified beforehand by evaluating an amount of ups anddowns of roads on which the vehicle is planning to travel.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIGS. 11 and 12.

In the present embodiment, the view point, which was established abovein the air and behind the vehicle in the previous embodiments, is nowestablished inside the vehicle. Concretely, the height of the view point11-2 established inside the vehicle 11-1, which is moving on the groundof elevation h from sea level, is determined by adding the elevation hof the vehicle's current location and a predetermined height Yi. Theview point established inside the vehicle will be called aninside-vehicle view point hereafter.

The procedure in the present embodiment is basically the same as that ofFIG. 7 with the predetermined height Y being replaced with Yi in Step7300, and makes it possible to establish the inside-vehicle view point.Further in the present embodiment, Steps 7400 and 7500 of FIG. 7 may beeliminated since the view point is always set above the ground plane atStep 7300.

Alternatively, the height Yi may be defined as a variable so that itsvalue may be adjusted in response to the type of vehicle or a vehicleheight which is inputted or selected by the user using the input device1-5.

FIG. 12 illustrates an example 12-1 of the display showing a sceneryimage near an intersection with the inside-vehicle view point. Thedisplay example 12-1 also shows a part of the vehicle structure, whichmay be seen by the driver (user) when he or she is looking out from theinside of the vehicle, such as a front glass frame 12-2 and rear viewmirror 12-3, superimposed on the scenery image. The part of vehiclestructure may be graphically generated using its structural data whichmay be stored in a storage device such as the map database device 1-3 orthe ROM 2-3.

Displaying the part of the vehicle structure superposed on the sceneryimage enables the user to relate an actual view from inside the vehicleand the displayed roads and buildings more easily, and thus increase therecognizability. Alternatively, the navigation system may be structuredin such a way that the input device 1-5 accepts the user's selectionregarding which part of the vehicle structure should be displayed, andthe display image is generated according to the user's selection.Further, the display with more clarity may be realized by additionallyexecuting transparent processing during the display procedure.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIG. 13.

The procedure of the present embodiment includes steps, in addition tothe procedure illustrated in FIG. 7, for switching a location of theview point between inside and outside the vehicle depending on a viewpoint height requested by the user. Further in the present embodiment,the input device 1-5 is structured so as to be able to accept aselection or switching operation from the user for changing the viewpoint height stepwise.

In the present procedure, the view point height y_(v) requested by theuser is obtained (Step 1310), and then it is checked if the view pointheight y_(v) is less than a predetermined height Y1 (Step 1320). If itis less than Y1, the view point height y_(v) is established inside thevehicle using the method described with reference to FIG. 11 (Step1330), and the line of sight is set along the moving direction of thevehicle (Step 1340).

If the view point height y_(v) is not less than Y1 in Step 1320, theview point height y_(v) is further checked to see if it is larger thananother predetermined height Y2 (Step 1350). If it is larger than Y2,the line of sight is set in a direction vertical to the ground plane atsea level 6-4 (Step 1360). If the view point height y_(v) is not lessthan Y1 and not larger than Y2, the view point height and a direction ofthe line of sight are determined using Steps 7200-7700 of FIG. 7.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIG. 14.

The procedure of the present embodiment includes steps for switching alocation of the view point between inside and outside the vehicledepending on a map display scale requested by the user, in addition tothe procedure illustrated in FIG. 7. Further in the present embodiment,the input device 1-5 is structured so as to be able to accept aselection or switching operation from the user for changing the mapdisplay scale stepwise. Further, Steps 1430, 1440, 1460 in the presentprocedure are the same as Steps 1330, 1340, 1360 in the procedure shownin FIG. 13, respectively.

In the present procedure, the display scale s requested by the user isobtained (Step 1410), and then the display scale s is checked to see ifit is less than a predetermined scale S1 (Step 1420). If it is less thanS1, the view point height y_(v) is established inside the vehicle usingthe method described with reference to FIG. 11 (Step 1430), and the lineof sight is set along the moving direction of the vehicle (Step 1440).

If the display scale s is not less than S1 in Step 1420, the displayscale s is further checked to see if it is larger than anotherpredetermined scale S2 (Step 1450). If it is larger than S2, the line ofsight is set in a direction vertical to the ground plane at sea level6-4 (Step 1460). If the display scale s is not less than S1 and notlarger than S2, the view point height and a direction of the line ofsight are determined using Steps 7200-7700 of FIG. 7.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIG. 15.

The procedure of the present embodiment includes steps which make itpossible to switch a view angle for displaying the map according to auser request regarding variables such as a display format of the displaydevice 1-2, in addition to the procedure illustrated in FIG. 7. Furtherin the present embodiment, the input device 1-5 is structured so as tobe able to select either a wide display mode or a normal display modefor setting the view angle of the display.

First, in the present procedure, the view angle requested by the user isobtained (Step 1510), and a value of the view angle is checked so as todecide whether the display mode should be in the wide mode or the normalmode (Step 1520). If the normal display mode is selected, the view angleis set at a default value (Step 1530). If the wide display mode isselected, the view angle is set to a larger value than the default viewangle (Step 1540). The procedure then proceeds to Step 7200 of FIG. 7for determining the view point height and a direction of the line ofsight.

The display size may be changed to a wider shape, for example, like thedisplay example 12-1 shown in FIG. 12. Further, the switching proceduresillustrated in FIGS. 13 and 14 for switching the view point betweeninside and outside the vehicle may be utilized in the present procedureso as to change the view angle in response to the switching of the viewpoint location.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIGS. 16, 17A and 17B.

The procedure of the present embodiment includes steps for switching theview point in response to switching of the display method between athree dimensional display and a pseudo three dimensional displayaccording to the user request, in addition to the procedure illustratedin FIG. 7. In the present specification, the three dimensional displaymethod means a method for displaying a stereoscopic three dimensionalmap using the map information containing height information such as theelevation or the like, and the pseudo three dimensional display methodmeans a method for generating a map image from the two dimensional mapinformation through the perspective transformation so as to display themap which makes it possible to give a distinctive impression ofdistance.

Further in the present embodiment, the input device 1-5 is structured soas to be able to accept a request from the user for selecting either oneof the three dimensional display and the pseudo three dimensionaldisplay. Step 7710 of the present procedure is the same as Step 7700 ofFIG. 7.

In the present procedure, the display method requested by the user isobtained (Step 1610), and it is then decided if the display should beexecuted by the three dimensional display method or the pseudo threedimensional display method (Step 1620). If the three dimensional displaymethod is selected, the procedure proceeds to Step 7200 of FIG. 7.There, as shown in FIG. 17A, the view point height y_(v) is determinedbased on the topographic elevation h_(t) at the vehicle's currentlocation 8-3 and the predetermined height Y, and the view point 8-4 isset at a location behind the vehicle separated by the predetermineddistance L with the view point height determined by Steps 7200-7700. Ifthe pseudo three dimensional display method is selected, the view point17-2 is set at a location behind the vehicle's current location 17-1separated by the predetermined distance L and the predetermined height Yabove sea level (Step 1630), and the line of sight is set along adirection toward the vehicle from the established view point (Step7710).

The display processing unit 3-10 generates graphic data for displaying aperspective map viewed from the view point established in the aboveprocedure using the display method selected by the user, and outputs thegraphic data to the display device 1-2.

Alternatively, the procedure may be structured so that the height Yabove sea level 6-4 may be switched to a fixed value during theswitching of the display method in the present procedure.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIG. 18.

The procedure of the present embodiment includes steps for switching theview point to a location 8-4 or 17-2 of FIGS. 17A and 17B in response toa scroll request from the user, in addition to the procedure illustratedin FIG. 7. Further in the present embodiment, the input device 1-5 isstructured so as to be able to accept a scroll request operation enteredby the user. Step 7110 in the present procedure is the same as Step 7100of FIG. 7.

In the present procedure, the vehicle's current location is obtained(Step 7110), and then it is decided if the user requests the scrolloperation (Step 7111). If the scroll operation is requested, the viewpoint 17-2 is set as shown in FIG. 17B at a predetermined height abovethe ground plane at sea level (Step 7112), and the line of sight fromthe view point is set along the scrolling direction (Step 7113).

In the present embodiment, the view point setting unit 3-11 establishesthe view point height with respect to sea level when a scroll buttondisposed in the input device 1-5 is being pressed. A processing speedfor renewing the display image may be gradually increased when thescroll button is kept pressed. Alternatively, the procedure may bestructured so that a scroll speed or an elapse of time since the scrollbutton has been pressed may be checked if it is beyond a correspondingpredetermined value in Step 7111 when the display is controlled in sucha way that the display image is renewed at a constant period, and theabove switching procedure may be executed if the scroll speed or theelapse of time is beyond the corresponding predetermined value.

An example of data structure in the map database device 1-3 of thepresent invention will now be described.

Map data of the present example comprises a data management unit 19-1and a data unit 19-2 as illustrated in FIG. 19. The map data may bemanaged, for example, using a “standard area mesh” which is obtained bydividing a total area with longitude and latitude lines separated fromeach other by fixed amounts. An identification number called a mesh codeis given to each of the standard area mesh.

The data management unit 19-1 stores a plurality of management tableseach corresponding to a respective one of the standard area meshes. Eachof the management table stores the mesh code 19-3, attribute information19-4, an elevation data management unit 19-5, a road data managementunit 19-6, a building data management unit 19-7, and the like.

The attribute information 19-4 stores a scale of the map, a date of themap data generation, and a number/name of the map. The elevation datamanagement unit 19-5 stores link destinations in an elevation data 19-8.The elevation data 19-8 comprises elevation values sampled at locationswhich are equally separated from each other in the standard area mesh,and makes it possible to generate a display image of its topographicalfeature.

The road data management unit 19-6 stores link destinations in a roaddata 19-9 in a similar way. The road data 19-9 stores link informationconnecting intersections (nodes), node coordinates, attributeinformation identifying a type of road such as a toll road or a nationalroad, road height information, and the like. Further, the building datamanagement unit 19-7 stores link destinations in building data 19-10.The building data 19-10 stores information such as names, shapes, andheights of the buildings.

Further, identification codes will be stored for indicating availabilityof no link destination in the road/building elevation information storedin one of the data management units 19-5-19-7 and the data 19-8-19-10due to the lack of the corresponding data.

A further embodiment of the procedure of the view point setting unit3-11 of the present invention will now be described with reference toFIGS. 20-22.

The procedure of the present embodiment includes steps for switching theview point in response to the above described identification codes,which may be obtained by utilizing the map database device 1-3 with thedata structure described in FIG. 19, in addition to the procedureillustrated in FIG. 7.

FIG. 20 shows an example of the procedure for switching the view pointin response to detection of elevation information of the topographicfeature (elevation data). Steps 7110, 7710 and 7123 in the presentprocedure are the same as Steps 7100, 7700 of FIG. 7 and Step 1630 ofFIG. 16 respectively.

In the present procedure, the map management information 19-3-19-7 ofthe standard area mesh corresponding to an area in the vicinity of thevehicle's current location are fetched from the map database device 1-3,and contents of the map management information are obtained (Step 7121).Further, it is decided if the elevation information of topographicalfeature is available or not in the corresponding standard area mesh bychecking the elevation data management unit 19-5 of the obtained mapinformation (Step 7122).

If the elevation information of topographic feature is available, theprocedure proceeds to Step 7200 of FIG. 7, and establishes the viewpoint and the line of sight for the three dimensional display accordingto Steps 7200-7700. If the elevation information of topographic featureis not available, the procedure proceeds to Step 7123 to set the viewpoint for the pseudo three dimensional display at the location 17-2 ofFIG. 17B and the line of sight along a direction toward to the vehicle(Step 7710).

FIG. 21 illustrates an example of the procedure for switching the viewpoint in response to detection of the elevation information of the road.FIG. 22 is an explanatory illustration supplementing FIG. 21. Theprocedure of the present embodiment includes Steps 7231, 7232 inaddition to the procedure illustrated in FIG. 7. In the presentprocedure, these additional steps are placed after Step 7200 of FIG. 7,and the vehicle is assumed to be located at a location 22-1 of FIG. 22.

In the present procedure, it is decided if the elevation information ofroad is available or not by checking the road data 19-9 included in theobtained map information at the vehicle's current location 22-1 (Step7231). If the road elevation hd 22-3 is available, the view point heightyv is calculated from the road elevation hd, the topographic elevation hand the predetermined height Y (Step 7232), and the view point 22-2 isestablished behind the vehicle with the predetermined separation L. Ifthe road elevation hd is not available, the view point is establishedaccording to Steps 7300-7700.

Alternatively, when data from a plurality of meshes are simultaneouslydeveloped into a display image, the procedure may be structured so as toset the view point 17-2 for the pseudo three dimensional display if themesh with no elevation data of topographic feature is included.

Further, if the map database includes identification information foridentifying a section of a road which is located inside a tunnel, theprocedure may be structured so as to switch the view point to theinside-vehicle view point using the identification information fordeciding when the road section where the vehicle is currently moving isidentified as inside the tunnel.

A further embodiment of the map display method of the present inventionwill be described with reference to FIGS. 23A and 23B.

In the present embodiment of the map display method, ashape/color/pattern/size of the vehicle's display image is varied inresponse to a change in the display setting condition such as the viewpoint, the line of sight, the view angle and the like.

To be concrete, the vehicle symbol may be displayed in a simple form asshown in FIG. 23A when the view point is set at a higher or distantlocation to the vehicle, and displayed in a stereoscopic form as shownin FIG. 23B when the view point is set at a lower or closer location tothe vehicle.

The above process may be realized by switching structural data of thevehicle symbol to be used, for example, according to a result of thedecision at Step 1320 or 1350 in FIG. 13, as further illustrated in FIG.25 as Step 1355 and Step 1370. Further, the display form of the vehiclesymbol may be changed in response to the switching of the display methodbetween the three dimensional display and the pseudo three dimensionaldisplay if the change of the vehicle's display form is executeddepending on a result of the decision at Step 1620 in FIG. 16. Thisprocess is further illustrated in FIG. 26 as Step 1640 and Step 1650.

According to the present invention as described above, the map dataincluding topographic features, roads, and buildings in the vicinity ofthe current location of the vehicle is read from the map database as thevehicle moves, and the view point is continuously renewed so as to beestablished at a point which is higher than the elevation of topographicfeature in the vicinity of the vehicle's current location. Therefore, itis possible to provide the navigation system which makes it possible tomaintain the view point above the ground surface even with thetopographical variation, and renew the scenery image smoothly with thevehicle's motion.

In the above mentioned embodiments, the map display methods employed inthe navigation system with the structure shown in FIG. 1 are describedas examples. However, the map display method of the present invention isnot limited to these embodiments. For example, a system may be realizedby storing programs for executing the map display method in storagemedia such as floppy disks, CDs or the like, and loading the programsinto a conventional computer system for executing the loaded programs.

Concretely, a map display apparatus may be realized for executingvarious map display methods mentioned above by storing a map displayprogram for executing the map display method of the present inventioninto a storage medium 24-2, and loading the map display program into acomputer system comprising a central operation and processing device24-1, a display 24-5 and an input device 24-6 for executing the mapdisplay program. There, the map database 24-3 is connected to thecomputer system for providing map information, and location information24-4 indicating a location to be displayed is fed to the computersystem. The location information may be provided, for example, from aGPS card which is connected to a computer and functions as a GPSreceiver.

In the above embodiments, the navigation system for an automobile isassumed as an example of the present invention. However, the presentinvention is also applicable to a portable navigation system for othertypes of moving object such as a person, who may use the system duringtrekking or the like in the same way as the previous embodiments.

According to the present invention, it is possible to provide a mapdisplay method and apparatus which makes it possible to display astereoscopic map image based on three dimensional map information.

Further, according to the present invention, it is possible to provide anavigation system having a function to display a stereoscopic map image,which makes it possible to renew a scenery image smoothly with movementof the vehicle, regardless of topographic variation.

What is claimed is:
 1. A map display apparatus for displaying a map on amoving display device, comprising: a data reading-out portion forreading out map data representing a mesh area comprising a first pointcorresponding to a positional information inputted from outside, from amap database that stores at least one of a first map data representing athree-dimensional map within said mesh area and a second map datarepresenting a two-dimensional map within said mesh area; a viewpointsetting portion for determining a viewpoint at an objective height withrespect to a second point, based on a height of the first point and aheight of the second point located a predetermined distance from thefirst point, when the data reading-out portion reads out a first mapdata, and for determining a viewpoint at a predetermined height withrespect to a third point located a predetermined distance from the firstpoint, when the data reading-out portion reads out a second map data;and a display processing portion for performing a perspectivetransformation on the map data, which is read out by the datareading-out portion from the viewpoint determined by said viewpointsetting portion, and for displaying graphics data generated by theperspective transformation on the display device; wherein a mode of amark representing said moving display device is switched in accordancewith a result whether the data reading-out portion reads out a first mapdata or a second map data, the mark being displayed on the displayapparatus superposing the graphics data.
 2. A map display apparatus fordisplaying a map on a display device, being mounted on a moving object,comprising: a data reading-out portion for reading out map datarepresenting a mesh area including a first point corresponding to apositional information inputted from outside, from a map database thatstores map data; a viewpoint setting portion for determining a viewpointat an objective height with respect to a second point based on a heightof the first point and a height of the second point at a location apredetermined distance from the first point, and for determining aviewpoint at a predetermined height with respect to a third point, at alocation a predetermined distance from the first point; and a displayprocessing portion for performing a perspective transformation on themap data from the viewpoint and for displaying graphic data generated bythe perspective transformation on the display device; wherein a mode ofa mark representing said moving object is switched in accordance with aresult whether the mark being displayed in the display apparatus in asuperposing manner on the graphics data.
 3. A map display apparatus fordisplaying a map on a display device, being mounted on a moving object,comprising: a data reading-out portion for reading out map datarepresenting a three-dimensional map within a mesh area including afirst point corresponding to a positional information inputted fromoutside, from a map database that stores said map data including heightdata and two-dimensional data within said mesh area; a viewpoint settingportion for determining a first viewpoint at an objective height withrespect to a second point based on a height of the first point and aheight of the second point at a location a predetermined distance formthe first point, in a three-dimensional display mode, and fordetermining a second viewpoint at a predetermined height with respect toa third point, at a location a predetermined distance from the firstpoint, in a pseudo three-dimensional display mode; and a displayprocessing portion for performing a perspective transformation on themap data from the first viewpoint in said three-dimensional display modeand performing a perspective transformation on the two-dimensional datain the map data from the second viewpoint in said pseudothree-dimensional display mode, and for displaying graphic datagenerated by the perspective transformation on the display device;wherein a mode of a mark representing said moving object is switched inaccordance with a result whether display mode is said three-dimensionaldisplay mode or said pseudo three-dimensional display mode, the markbeing displayed in the display apparatus in a superposing manner on thegraphics data.
 4. A map display apparatus in accordance with claim 1,wherein said mode of said mark is switched to a stereoscopic form in acase where the map data read out by the data reading-out portion is thefirst map data, and said mode of said mark is switched to a simple formin a case where the map data read out by the data reading-out portion isthe second map data.
 5. A map display apparatus in accordance with claim3, wherein said mode of said mark is switched to a stereoscopic form insaid three-dimensional display mode, and said mode of said mark isswitched to a simple form in said pseudo three-dimensional display mode.6. A map display apparatus in accordance with claim 3, furthercomprising an input device for accepting a request for selecting eitherone of said three-dimensional display mode and said pseudothree-dimensional display mode.
 7. A map display apparatus fordisplaying a map on a display device, being mounted on a moving object,comprising: a data reading-out portion for reading out map datarepresenting a three-dimensional map within a mesh area including afirst point corresponding to a positional information inputted fromoutside, from a map database that stores said map data; a viewpointsetting portion for determining a view point at an objecting height withrespect to a second point, based on a height of the first point and aheight of the second point at a location a predetermined distance fromthe first point; an input device for accepting an operation for changingsaid height of said viewpoint, said viewpoint setting portion changingsaid height of said viewpoint in response to said operation; a displayprocessing portion for performing a perspective transformation the mapdata read out by the data reading-out portion from the viewpoint, andfor displaying graphics data generated by the perspective transformationon the display device; wherein a mode of a mark representing said movingobject is switched in accordance with said height of said viewpoint. 8.A map display apparatus in accordance with claim 7, wherein said mode ofsaid mark is switched to either one of a stereoscopic form and a simpleform, based on said height of said viewpoint.